In order to evaluate the effect of poloxamer 407 content on the dissolution profiles of pellets, diltiazem HCl (DTL) core pellets were prepared with poloxamer 407 (50-90% w/w, with lactose as filler) using an extruder and a spheronizer. Any possible interaction between the drug and excipients was evaluated using DSC, IR and TLC. Dissolution tests were performed using USP basket method. In addition, scanning electron micrograph was performed to examine the surface roughness and cross sections. The release of DTL from the core pellets was decreased with increasing poloxamer 407 content. Cracks appeared on the surface of the core pellets with increasing the poloxamer 407 content, which may play a role on the retardation of the release of DTL from core pellets. There was no any significant interaction between the drug and excipients employed to prepare the core pellets.